At the present time, the most promising areas of basic neuroscience research which may eventually lead to successful reconstructive neurosurgery involve the application of neurotrophic factors to rescue axotomized neurons from retrograde degeneration, neuronal transplantation to replace lost neural populations, and the use of antibodies directed against myelin-associated neurite growth inhibitors to improve axonal regeneration. Recently, several investigators have demonstrated that the intraventricular infusion of nerve growth factor (NGF) and the transplantation of genetically modified fibroblasts which produce NGF can rescue neurons in the medial septum from retrograde degeneration after lesioning of the fimbria fornix. The other neurotrophins (BDNF, NT-3, NT- 4, NT-5) and growth factors (CNTF, IGF-1) may also have similar effects on axotomized neurons in the basal forebrain. Since the cholinergic neurons in the basal forebrain undergo atrophy and degeneration in Alzheimer's disease, one strategy that could be potentially used to treat the disease is the delivery of neurotrophic factors to this region in an effort to decrease neuronal loss. The aim of the first project of this proposal is to generate a genetically modified cell line which produces and secretes neurotrophin-4 (NT-4), a neurotrophic factor which has a strong effect on cholinergic neuron survival and metabolism in tissue culture. The long-term growth characteristics, mRNA expression, and neurotrophic factor secretion will then be studied in a genetically modified cell line in vivo. Several manipulations of the cell line may be performed in order to produce a steady release of neurotrophic factor over an extended period of time and to ensure that uncontrolled fibroblast growth does not lead to an intracranial tumor. The cell lines will then be examined in vitro to determine the regulatory mechanisms of neurotrophic factor gene expression and protein synthesis. Finally, the effects of various genetically modified fibroblasts on the lesioned septo-hippocampal pathway will be studied in detail to determine which neurotrophin(s) should be utilized clinically to decrease cholinergic neuron degeneration in the basal forebrain in Alzheimer's disease. In summary, this proposal contains several projects which will answer questions concerning the growth characteristics, resulting mechanisms, and neurotrophic effects of genetically modified cell lines. Each of these issues needs to be addressed before genetically modified cell lines can be used to treat neurodegenerative diseases.